Cant get mbufs

[Phil Farrell]

In article <rcmart.675956786 at rwb.urc.tue.nl> rcmart at urc.tue.nl writes:
>
>Since a few days we have a very nasty problem on our DECsystem 5400,
>which runs under Ultrix 4.0.
>After a timeperiod of about 7 hours the system reports "cant get mbufs"
>on the console and then the system hangs!

"mbufs" are the memory areas used to queue incoming and outgoing ethernet 
packets.  You can see how many are in use with "vmstat -K".  The number 
allocated by the system is a function of the "physmem" and "maxusers"
kernel configuration parameters.  Perhaps your network load is simply
too great for the values you have configured into your kernel.  You could
try increasing either or both of these parameters and building a new
kernel.  By the way, DEC lore (that is, what the support engineers tell
you, not what the documentation says) is that the "physmem" parameter 
on RISC systems should not be set equal to the actual amount of physical
memory, but rather to at least 125% of actual memory in order to properly
size system tables, particularly the PTEs that map between physical and
virtual memory.  On the other hand, you may be seeing a pathological 
condition where mbufs are not being properly freed.  I can't help you 
with that possibility and have my doubts that DEC can either.

-Phil Farrell, Computer Systems Manager
Stanford University School of Earth Sciences
farrell at pangea.stanford.edu